Techniques were developed to examine the sensitivity of the ratio of the residence times of the two apoA-I components in the apoA-I model. Utilizing plasma, urine and whole body radioactivity data apoA-I and apoA-II compartmental models were constructed for both males and females. ApoA-II decayed by two pathways in both males and females. In males, 25% of apoA-II decayed through the minor pathway which took 22 hr. longer than the major decay pathway. In females, 30% was catabolized by the minor pathway with delay of 31 hrs. ApoA-I has two distinct plasma compartments in both males and females. Twenty eight percent of apoA-I is found in the second compartment for males, and 40% is present in females. In addition, while the second apoA-I component has the same residence time in males and females, the primary component in males has a residence time of 5.4 days and in females, 6.8 days. Triglyceride kinetics were studied in hyperlipidemic caucasian, and diabetic Pina Indians utilizing radiolabeled glycerol. Hypertriglyceridemia in subjects with genetically defined familial hyperlipidemia was associated with increased triglyceride production while in a group of patients with Type IV phenotype elevated triglycerides were secondary to decreased fractional catabolism.